Along with development of finer patterning in a semiconductor device, there has been occurring of the problem of a malfunction in the contact-hole processing by which contact plugs are formed. Examples of the malfunction in the contact-hole processing include an undesirable shape, insufficient etching or deposited residues after the etching for forming contact holes, and insufficient filling of the contact holes after deposition of contact plugs. In a conventional technique, if a suspected problem occurs at a specific location after the contact-hole processing, the specific location is inspected by a FIB-SEM processing including a FIB-etching processing and a subsequent inspection processing using a scanning electron microscope (SEM), or a FIB-TEM processing using a FIB-etching processing and a subsequent inspection processing using a transmission electron microscope (TEM).
In the up-to-date semiconductor manufacturing process, FIB-SEM systems having a FIB-SEM inspection function have become widely used, contributing to improvement in the analysis of the problem occurring therein. However, since this analysis requires a longer processing time and necessitates mastery of the skill for using the FIB-SEM system, there is a difficulty in the practical use of the FIB-SEM system in the semiconductor fabrication industry. FIG. 10 shows a typical FIB-SEM system used for inspection of a semiconductor wafer. In particular, the FIB-SEM systems now in widespread use generally have an angle of 30 to 60 degrees between the axis of the FIB device 21 and the axis of the SEM device 22, wherein the FIB device 21 is dedicated to etching of a wafer 23 by irradiating a FIB and the SEM device 22 is dedicated to inspection of the section of the wafer from an angled direction with respect to the axis of the FIB device. The FIB-SEM system is described in Patent Publication JP-2004-361140A, for example.
FIG. 11 is a flowchart showing the procedure of processing a semiconductor wafer by a conventional FIB-SEM system. In this processing, the FIB device performs a FIB-etching processing so that a desired section of the contact pattern including an array of contact plugs is exposed from the main surface of the wafer. The exposed section is generally perpendicular to the main surface of the wafer or at least intersects the main surface.
The FIB-etching processing includes the steps of setting coordinates for processing in accordance with an alignment mark of the wafer (step S1), and imaging the contact pattern on the wafer surface (step S2). The FIB-etching processing further includes the steps of setting the area for FIB-etching processing on the wafer surface as well as the beam conditions for the FIB etching (step S3). Thereafter, the FIB-etching processing is started using a scanning irradiation technique in a line-by-line basis within the area thus set (step S4). After the etching by the scanning irradiation is finished up to the specified location based on the location information on the wafer surface, the section of the pattern thus exposed from the wafer surface is subjected to an inspection to judge whether or not a desired section is obtained by the FIB-etching processing. If it is judged that a desired section is not yet obtained, a further FIB-etching processing is performed for correction of the exposed section (step S5).
As described above, it is difficult to obtain the desired exposed section in the FIB-etching processing merely from the location information on the wafer surface. That is, a desired exposed section generally necessitates correction of the exposed section based on an inspection by a user of the system. In addition, the judgment as to whether or not the desired exposed section is obtained and a judgment of subsequent correction depend on the skill of the user operating the FIB-SEM system. Thus, it is generally difficult to obtain a desired exposed section in the FIB-SEM system.
In view of the above problem in the conventional technique, it is an object of the present invention to provide a FIB-etching processing system and a FIB-etching processing method, which are capable of obtaining a desired exposed section in a semiconductor device, substantially without correction based on the judgment by a user.
The present invention provides a focused ion beam (FIB) processing system including: a FIB irradiation unit that irradiates a FIB onto a pattern formed in a wafer, to form a section of the pattern that intersects a top surface of the wafer; an imaging unit that images the section of the pattern; a calculation unit that calculates a pattern size based on the image of the section; a judgment unit that judges whether or not a differential of the pattern size with respect to time is equal to or below a threshold; and a control unit that stops the FIB irradiation unit if the judgment unit judges that the differential of the pattern size is equal to or below the threshold.
The present invention also provides a focused ion beam (FIB) processing system including: a FIB irradiation unit that irradiates a FIB onto a pattern formed in a wafer, to form a section of the pattern that intersects a top surface of the wafer; an imaging unit that images the section of the pattern; a calculation unit that calculates a pattern size based on the image of the section, to store in a storage device the pattern size in association with a time instant at which the section of the patter is imaged; a function unit that determines a time function of the pattern size based on the pattern size and time instant; and a control unit that controls a stop position of the FIB irradiation unit based on the time function.
The present invention further provides a focused ion beam (FIB) processing method including: irradiating a FIB onto a pattern formed in a wafer, to form a section of the pattern that intersects a top surface of the wafer; imaging the section of the pattern; calculating a pattern size on the section based on the image of the section; judging whether or not a differential of the pattern size with respect to time is equal to or below a threshold; and stopping the FIB irradiation if it is judged that the differential of the pattern size is equal to or below the threshold.
The present invention further provides a focused ion beam (FIB) processing method including: irradiating a FIB onto a pattern formed in a wafer, to form a section of the pattern that intersects a top surface of the wafer; imaging the section of the pattern; calculating a pattern size on the section based on the image of the section, to store the pattern size in association with a time instant at which the section of the pattern is imaged; determining a time function of the pattern size based on the pattern size and time instant; and controlling a stop position of the FIB irradiation based on the time function.
The above and other objects, features and advantages of the present invention will be more apparent from the following description, referring to the accompanying drawings.